KINETIC-ANALYSIS OF HUMAN T-CELL LEUKEMIA-VIRUS TYPE-I TAX-MEDIATED ACTIVATION OF NF-KAPPA-B

The human T-cell leukemia virus type I (HTLV-I) Tax protein induces th e expression of cellular genes, at least in part, by activating the en dogenous NF-kappa B transcription factors. Induced expression of cellu lar genes is thought to be important for transformation of T cells to continued growth, a prelude to the establishment of adult T-cell leuke mia. However, neither underlying mechanisms nor kinetics of the Tax-me diated activation of NF-kappa B are understood, We have analyzed a per manently transfected Jurkat T-cell line in which the expression of Tax is entirely dependent on addition of heavy metals. The initial NF-kap pa B binding activity seen after induction of Tax is due almost exclus ively to p50/p65 heterodimers. At later times, NF-kappa B complexes co ntaining c-Rel and/or p52 accumulate. The early activation of p50/p65 complexes is a posttranslational event, since neither mRNA nor protein levels of NF-kappa B subunits had increased at that time. We demonstr ate for the first time a Tax-induced proteolytic degradation of the NF -kappa B inhibitor, I kappa B-alpha, which may trigger the initial nuc lear translocation of NF-kappa B. As nuclear NF-kappa B rapidly and po tently stimulates resynthesis of I kappa B-alpha, the steady-state lev el of I kappa B-alpha does not significantly change, Thus, the dramati c Tax-induced increase in the I kappa B-alpha turnover may continually weaken inhibition and activate NF-kappa B. Additional, distinct actio ns of Tax may contribute further to the high levels of NP-kappa B acti vity seen,